This invention is related to an air sampling pump unit and in particular to an improved air sampling pump unit designed for use by an individual.
Air sampling pump units having a constant air flow rate are used to monitor air to which workers are exposed. These pump units are well known in the art. Typical examples of such pump units are shown in Baker et al. U.S. Pat. No. 4,063,824 issued Dec. 20, 1977, Baker et al. U.S. Pat. No. 4,123,932 issued Nov. 7, 1978, Wells U.S. Pat. No. 4,257,746 issued Mar. 24, 1981 and Baker U.S. Pat. No. 4,269,059 issued May 26, 1981. These pump units are excellent for the particular use for which the pump units were designed. However, there is a need for a versatile pump which can accurately pump air at very low flow rates such as 5 cc/min. to very high flow rates such as 5000 cc/min. Also, it would be desirable to have the following features on the pump unit: user programmable starting time, running time, and tolerated restricted air flow time; measure air temperature; have memory retention of program; have memory retention after the unit is turned off; have a liquid crystal display which shows values of flow, time and temperature and a computer interface which will allow loading of data into a computer and allow loading of operational data into the pump unit.
In the operation of the aforementioned prior art air sampling pump units, the pump is controlled through a pressure switch positioned in parallel to an orifice which monitors pressure drop across the orifice caused by a change in air flow. For example, if there is a blockage of air flow, the pressure switch closes and through an integrator circuit and an amplifier circuit provides an increased voltage to the motor driving the pump and thereby increases the air flow. When the pressure drop across the orifice returns to normal, the pressure switch opens and the pump operates under usual conditions. The pressure switch also constantly opens and closes with pulsations in air flow caused by pulsations of the pump. Under extremely severe operating conditions such as opening and closing of the switch several hundred times a minute, the electrodes of the pressure switch rapidly deteriorate because of electrical arcing across the electrodes. An improvement that is required would determine whether or not the switch was open or closed without applying a constant voltage across the switch to generate an electrical signal.
The improved air sampling pump unit of this invention pump units air accurately at very low and high rates, is user programmable to start and run for a period of time, measures temperatures, has a memory retention, a liquid crystal display and measures the on-off position of the pressure switch without applying a constant voltage across the switch and controls the air pump via a computer and allows for loading and unloading of data.